Effect of in situ prepared silica nano-particles on non-isothermal crystallization of polypropylene

The crystallization behavior of PP/silica nanocomposites prepared in-situ via solid-state modification and sol-gel reaction is investigated. The crystallization behavior studied with DSC shows that in situ formed silica nano-particles act as nucleating agents. The non-isothermal crystallization kinetics of PP/silica nanocomposites is studied using a combined Avrami-Ozawa approach and shows a two-stage crystallization process: the primary stage is characterized by nucleation and spherulitic growth and the secondary stage is characteristic of the perfectioning of crystals. Silica speeds up the primary stage, resulting in a more narrow lamellar thickness distribution. The crystallization activation energy decreases with increasing silica content in the PP/silica nanocomposites. The nucleating efficiency of the in-situ prepared silica particles based on the scale as proposed by Lotz and co-workers is found to be 20% in the low concentration range and is higher compared to silica nano-particles as well as other nano-fillers studied. The melting behavior indicates the formation of more perfect crystals with a narrow lamellar thickness distribution and the WAXD patterns show that silica nano-particles induce the formation of crystals with the β-modification in PP at high silica content (ca. 5 wt%). DMTA analysis shows a marginal lowering of the T_g and an increased mobility of the amorphous phase.     

Characterization of surface-modified montmorillonite nanocomposites

Montmorillonite K-10 clay was surface-modified using the cationic surfactants viz., butyltriphenylphosphonium bromide (BTPB), cetyltrimethylammonium bromide (CTAB), and tributylhexadecylphosphonium (TBHPB) bromide. Of these, CTAB and TBHPB modified clays were chosen for surface grafting with 3-aminopropyltrimethoxy silane (APTMS) coupling agent. The nanocomposites were fully characterized by powder X-ray diffraction (XRD), solid state ²⁹Si NMR, Fourier transform infrared spectroscopy (FTIR) and thermogravimetry (TGA). The XRD and FTIR confirmed the increase in basal plane spacing and intercalation of long chain surfactant molecules into the clay gallery, while TGA indicated the onset degradation and 10% weight loss temperature (T_10%) in case of quaternary phosphonium modified clay that was higher than the corresponding ammonium counterpart; these values increased further after the grafting with APTMS. The ²⁹Si NMR peak deconvolution study suggested that the molar % of T units and total degree of silica condensation for different APTMS grafted clay samples were more than 20% and 80%, respectively.     

Surface-grafted silica linked with l-lactic acid oligomer: A novel nanofiller to improve the performance of biodegradable poly(l-lactide)

A new surface modification method by grafting l-lactic acid oligomer onto the surface silanol groups of silica nanoparticles has been developed. The surface-grafting reaction is confirmed by IR and ²⁹Si MAS NMR analyses. TEM and SEM results show that grafted SiO₂ (g-SiO₂) nanoparticles can be comparatively uniformly dispersed in chloroform or PLLA matrix, while the unmodified SiO₂ nanoparticles tend to aggregate. The loading of g-SiO₂ nanoparticles in poly(l-lactide) (PLLA) matrix greatly improves the toughness and tensile strength of this material. In contrast, the incorporation of un-grafted SiO₂ nanoparticles into PLLA leads to the deterioration of its mechanical properties. DSC analysis shows that g-SiO₂ nanoparticles can serve as a nucleating agent for the crystallization of PLLA in the composites. SEM characterization shows the tough characteristics and great interfacial combination strength for g-SiO₂ (5 wt%)/PLLA nanocomposites.     

Synthesis and NMR Characterization of Titanium and Zirconium Oxides Incorporated in SBA-15

Single oxides of Ti and Zr incorporated SBA-15 were prepared and characterized by N₂ adsorption, NMR, and XPS techniques. ²⁹Si MAS NMR results suggest the formation of Si–O–X linkages (X: Ti or Zr) by an increase in the ratio of Q ³/Q ⁴ in the presence of Ti or Zr. XPS analysis of Ti–SBA-15 catalysts indicate the presence of Ti–O–Si bonds in addition to Ti–O–Ti and Si–O–Si bonds, supporting the NMR evidence.     

The heterogenization of l-phenylalanine–Ru(III) complex and its application as catalyst in esterification of ethyl alcohol with acetic acid

A simple route is demonstrated for the efficient immobilization of silica with l-(N-α-acetylphenylalanine)–ruthenium(III) complex. This catalyst was labelled as RHAPhe–Ru. The ²⁹Si MAS NMR showed the presence of T³, T², Q³ and Q⁴ silicon centers. The ¹³C MAS NMR showed the presence of three chemical shifts consistent with the three carbon atoms of the propyl group. The catalytic performance of RHAPhe–Ru was tested in the esterification of ethyl alcohol. A conversion of 82% was achieved, with 100% selectivity towards ethyl acetate. The catalyst could be regenerated by washing with ethanol and drying at 110 °C for 24 h without significant loss in reactivity.     

Synthesis and characterization of poly(methyl methacrylate)‐grafted silica microparticles

A procedure to synthesize poly(methyl methacrylate)‐grafted silica microparticles was developed by using radical photopolymerization of methyl methacrylate (MMA) initiated from N,N‐diethyldithiocarbamate (DEDT) groups previously bound to the silica surface (grafting “from”). The functionalization of silica microparticles with DEDT groups was performed in two steps: introduction of chlorinated functions onto the surface of silica particles, and then nucleophilic substitution of chlorines by DEDT functions via a S_N2 mechanism. The study was performed with a Kieselgel® S silica which was initially chlorinated in surface, either by direct chlorination of silanols with thionyl chloride, or by using a condensation reaction between silanols and a chlorofunctional trialkoxysilane reagent, 4‐(chloromethyl)phenyltrimethoxysilane and chloromethyltriethoxysilane, respectively. Three types of DEDT‐functionalized silica microparticles were prepared with a good control of the reactions, and then characterized by solid‐state ¹³C and ²⁹Si CP/MAS NMR. Their ability to initiate MMA photopolymerization was studied. The kinetics of MMA photopolymerization was followed by HPLC and ¹H‐NMR. Whatever the silica used the grafting progresses very slowly. On the other hand, the conversion of MMA in PMMA grafts is depending on the structure of the DEDT‐functionalized Kieselgel® S used. Poly(methyl methacrylate)‐grafted silica microparticles bearing high length grafts ( about 100) were synthesized. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Highly dispersed zinc phosphate microdomains in mesoporous silica

In situ immobilization of crystalline zinc phosphate nuclei in the mesoporous silica material resulted in a highly ordered 2D-hexagonal mesoporous material with evenly dispersed crystalline NaZnPO₄ microdomains in its matrix using the self-assembly of cationic surfactant under hydrothermal synthesis condition. Four samples with different Si:Zn:P:Na mole ratios have been prepared. X-ray diffraction (XRD) patterns of the as-synthesized as well as template-free samples indicated the presence of mesophase in each case. N₂ adsorption data indicated mesoporosity in the samples together with the existence of crystalline NaZnPO₄ phase for the materials synthesized with Si/Zn mole ratio 5-12. ²⁹Si MAS NMR results showed high value of the Q⁴/Q³ ratio in these materials suggesting highly crosslinked structure.     

Spectroscopy characteristics for interlamellar silylation of H+-titanosilicate using dodecylamine and octyltriethoxysilane

Titanosilicate was modified by interlayer surface silylation using octyltriethoxysilane (OTES) and dodecylamine (DDA) in ethanol without a pre-swelling step. The introduction of silyl groups into the interlayer region was confirmed by XRD, FT-IR, RAMAN, SEM, TGA, ²⁹Si NMR and TEM. DDA acts as a gallery expander and silylation catalyst. The evaporation of ethanol from the dispersion yields well-ordered silylation. Layered titanosilicate silicate with large basal spacings between 2.95 and 3.87 nm were investigated. The layered structures of the silylated products were confirmed by swelling behavior upon attachment of alkylsilyl groups. Solid-state ²⁹Si MAS NMR of the silylated samples showed Q³ and Q⁴ signals as well as T² signals. The increase in the relative intensity of Q⁴ for Q³ and the appearance of a T² signal was attributed to the grafting of OTES to the interlayer surface silanol groups. This method provides a promising route for the preparation of new functional nanomaterials to bond a variety of functional groups to the interlayer surface of layered materials.     

Atom transfer radical polymerization from silica nanoparticles using the ‘grafting from’ method and structural study via small-angle neutron scattering

Polymer chains were grafted from silica beads (colloidal sol in dimethylacetamide) by atom transfer radical polymerization (ATRP), via the ‘grafting from’ method. The grafting of the initiator onto the silica surface was done in two steps. First, thiol-functionalization of the surface was achieved via silanization with a mercaptopropyl triethoxysilane. Second, we performed an over-grafting of the surface by reacting the thiol with 2-bromoisobutyryl bromide to generate the halogen-functional ATRP initiator. The nanoparticles were kept in solution (in the same solvent) at each stage of the functionalization (even during the purification steps), as this is the only way to avoid irreversible aggregation. Then, the polymerization of styrene was conducted. Control of both the molecular weight and the density of grafted chains can be achieved by this method. Careful characterization such as gel permeation chromatography, ²⁹Si CP/MAS NMR, elemental analysis, infrared spectroscopy and thermo-gravimetric analysis is performed. The state of dispersion of the grafted nanoparticles is followed in details by small angle neutron scattering and results obtained from this technique are presented here as well as the way the SANS data can be treated. Connection is systematically done between the information provided by this technique and the improvement of the synthetic procedure.     

Grafting of polystyrene chains on surfaces of nanosilica particles via peroxide bulk polymerization

This article describes an in situ bulk polymerization process of styrene in the presence of silica nanoparticles. In this peroxide bulk polymerization process, two polystyrene fractions are formed: A polystyrene (PS) fraction attached to the particle's surface, which cannot be detached by hot xylene extraction, and an unattached PS fraction which dissolves in xylene. Solvent extraction and TGA measurements have confirmed the existence of grafted PS chains to the silica surfaces. FTIR measurements have indicated the existence of Si O C bonds connecting the PS grafts to the silica surface. Polypropylene (PP) was blended with the extracted PS‐g‐silica particles to produce concentrations of 1–3% nanoparticles in the PP composites. A remarkably improved dispersability of the nanoparticles was achieved, thus grafting reduces re‐agglomeration and increases the affinity of the grafted surface to the polymer matrix. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

碱性嫁接型离子液体催化二氧化碳环加成反应

采用后嫁接法将不同量的1-甲基-3-丙基(三乙氧基硅基)咪唑的氢氧化物(［Smim］OH)嫁接到介孔硅胶(SiO₂)上,采用傅里叶变换红外光谱、元素分析、硅核磁共振及热重分析等技术对所制备的材料进行表征。在无溶剂、温和的条件下,将碱性嫁接型离子液体用于CO₂与环氧丙烷(PO)合成碳酸丙烯酯(PC)的环加成反应来考察其催化活性。结果表明,离子液体［Smim］OH成功地以共价键嫁接到介孔硅胶上得到碱性嫁接型离子液体(GILs),但不同量的［Smim］OH嫁接程度有所不同;在优化条件下,PO的转化率为99.5%,选择性为100%。反应后催化剂经过滤即可分离回收利用,且多次使用仍保持较高的反应活性。     

Double organic modification by 3‐chloropropyl and methyl groups on pure silica MCM‐41 and Ti‐MCM‐41: efficient catalyst for epoxidation of cyclododecene

Simultaneous surface modification by 3‐chloropropyl and methyl groups on the same Si atoms resulted in hydrophobic and highly ordered mesoporous silica with a very high surface area. ¹³C and ²⁹Si MAS NMR spectra indicate homogeneous grafting of chloropropyl and methyl groups in the silica matrix and this organically modified Ti‐MCM‐41 shows outstanding catalytic performance in the epoxidation of cyclododecene using tert‐butyl hydroperoxide as oxidant. This revised version was published online in July 2006 with corrections to the Cover Date.     

Functional polymers supported on porous silica. II.Radical polymerization of vinylbenzyl chloride from grafted precursors

Vinylbenzyl chloride was chosen as a model monomer for grafting a functional polymer onto silica carrying radical active precursors, such as monomer, transfer agent or initiator, previously grafted onto silica via a suitable coupling agent. The grafting efficiency was studied as a function of the texture of the initial silica, the nature of the active precursor and the polymerization conditions. Evidence for grafting was obtained from FTIR and ²⁹Si CP-MAS NMR spectra, and the thickness of the grafted layer was estimated from surface area and porosimetry measurements. From molecular weight measurements of nongrafted polymer it can be deduced that there is a trend toward the elongated conformation of the grafted polymer. Attempts to separate the grafted polymer through digestion of the silica with HF, failed to give a soluble linear polymer except when the active precursor was a transfer agent; in the two other cases a crosslinked polymer with a low crosslink density was obtained, which kept the morphology of the initial silica.     

Development of amidoxime functionalized silica by radiation‐induced grafting

A novel amidoxime‐based silica adsorbent was prepared by using radiation‐induced grafting technique. Grafting of acrylonitrile (AN) on silanized silica that was silanized by vinyltriethoxysilane (VTES) was carried out in solvent‐free system. The grafting of AN was increased with increasing the absorbed dose and monomer concentration in the mixture. Grafting of 748% of AN was achieved at 20 kGy dose. The nitrile groups of acrylonitrile grafted silica (AN‐g‐S) were chemically converted into amidoxime groups. The structure of AN‐g‐S and its corresponding products was investigated by FTIR, SEM, TGA, BET, and XRD analysis. FTIR and EDX analysis confirmed the grafting of AN onto silica surface. The changed morphology of SEM images shows the presence polyacrylonitrile layers on silica particles. The adsorption application of amidoxime‐grafted silica (AO‐g‐S) was studied against Cu²⁺. Its adsorption capacity is strongly depended on the pH of the solution and 172 (mg/g) of Cu²⁺ uptake was obtained at pH 5.0. The developed adsorbent has potential application to remove heavy metal ions from aqueous solutions. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45437.     

Study of the morphology and mechanical properties of polypropylene composites with silica or rice‐husk

The mechanical, morphological behavior and water absorption characteristics of polypropylene (PP) and silica, or PP and rice‐husk, composites have been studied. The silica used in this study as filler was a commercial type produced from soluble glass or rice husks. The compatibilizing effect of PP grafted with monomethyl itaconate (PP‐g‐MMI) and/or with vinyltriethoxysilane (PP‐g‐VTES) as polar monomers on the mechanical properties and water absorption was also investigated. In general, a high loading of the studied fillers in the polymer matrix increases the stiffness and the water absorption capacity. This effect is more noticeable in the tensile modulus of the PP/silica composite with PP‐g‐VTES as compatibilizer. However, the increase of the rice‐husk charge as a natural filler in the PP matrix decreases the stiffness, and in the presence of PP‐g‐MMI as compatibilizer in PP/rice‐husk, the tensile modulus and water absorption of the composite were improved. The better adhesion and phase continuity in the PP/silica and PP/rice‐husk composites with different compatibilizers was confirmed by the morphological study. Copyright © 2004 Society of Chemical Industry     

Quantification of silane grafting efficacy,weak IR vibration bands and percentage crystallinity in post e-beam irradiated UHMWPE

Vinyl-tri-methoxy silane (VTMS) and vinyl-tri-ethoxy silane (VTES) were grafted onto ultra-high molecular weight polyethylene (UHMWPE) by irradiating the UHMWPE/silane hybrids with e-beam. The samples were irradiated under high moisture contents for total dose values of 30, 65 and 100 kGy, respectively. The synergistic effect of silane and irradiation on the grafting efficacy, concentration of weak bonds like trans-vinylene (–CH=CH–) and vinyl (–CH=CH₂) and percentage values of crystallinity were studied using FTIR spectroscopy. For the estimation of grafting reactions efficiency, absorption due to characteristic infrared absorption bands of –Si–CH– in the region ~800 cm^?1 was monitored and found that grafting efficacy of VTMS on UHMWPE was higher as compared to VTES and increased with irradiation. The relative amounts of grafting extension (R) for 100 kGy irradiated UHMWPE/VTMS and UHMWPE/VTES hybrids were found to increase 20 and 15 %, respectively. The concentration of trans-vinylene in UHMWPE was found to increase from 0.015 to 0.035 mmol/l due to synergistic effects of silane and irradiation. Moreover, crystallinity of UHWMPE was found to decrease from 65 to 55 % due to the abovementioned synergistic effects which was also confirmed with DSC tests. Furthermore, oxidation index values were measured to confirm the efficacy of silane as free radical quencher via silane grafting extension reactions.     

Synthesis and grafting ability of silane-terminated polyethylenes on silica surfaces

Chlorosilane-terminated polyethylenes having different molar masses are prepared to be used as connecting molecules between a silica surface and a neat polyethylene matrix. The synthesis and the grafting ability of such functionalized polyethylenes is reported. The grafting efficiency is demonstrated by means of ²⁹Si NMR and wetting measurements according to the hydrophobic nature of the grafted molecules in comparison with the hydrophilic character of the silica surface. The resulting thickness and refractive index of the dry grafted layers are characterized using spectroscopic ellipsometry. The grafting ratios are given from microanalysis measurements. Surface topography is observed using AFM. All of these techniques are in a good agreement and a general trend of the organization of the tethered layers at the surface is proposed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2481–2492, 1997     

Octadecyl grafted MCM-41 silica spheres using trifunctionalsilane precursors – preparation and characterization

MCM-41 silica spheres were prepared via the pseudomorphic route. Subsequent surface modification of the mesoporous silica spheres was achieved by two silylating agents, n-octadecyltrihydridosilane and n-octadecyltrimethoxysilane, which provided different surface coverages. The MCM-41 pore structure, surface properties and morphological features were examined by small angle X-ray scattering, nitrogen adsorption–desorption and scanning electron microscopy. The investigations revealed an influence of the silica source on the mesoporous structure, as reflected by a higher long-range order for the pores in MCM-41 spheres prepared from Kromasil silica. Surface modification is accompanied by a reduction of the surface area, pore diameter and pore volume of the MCM-41 materials, whereas the spherical morphology of the spheres is retained. The degree of grafting and cross-linking of the alkylsilanes was determined by ²⁹Si NMR spectroscopy. A higher degree of alkyl chain grafting was observed for the solvent extracted MCM-41 spheres and for samples prepared via surface polymerization.FTIR and ¹³C NMR spectroscopies were employed to study the conformational behaviour and mobility of the grafted octadecyl chains. The conformational order was found to strongly depend on the history of the MCM-41 supports (calcination, solvent extraction) and on the actual surface modification procedure. In general, a lower conformational order was observed for the present mesoporous alkyl modified silica spheres as compared to conventional C₁₈ modified silica gels which is mainly attributed to the lower surface coverage.     

原位溶胶-凝胶法改性EPDM及其表征

采用原位溶胶-凝胶反应制备乙丙橡胶/ SiO₂纳米复合材料。分别以乙丙橡胶（EPDM）和γ-甲基丙烯酰氧丙基三甲氧基硅烷（KH570）接枝改性的乙丙橡胶 （EPDM-g-KH570）在前驱体四乙氧基硅烷 （TEOS）中溶胀,再浸入含有正丁胺的催化剂溶液中催化前驱体的原位溶胶-凝胶反应。考察了不同溶剂以及催化剂含量对TEOS转化率和原位生成的SiO₂粒径的影响。采用FT-IR、SEM等测试手段对纳米复合材料进行了表征。结果表明,接枝KH570后,TEOS转化率明显提高,SiO₂粒径明显减小,在材料中的分散性很好。     

Molecular shape recognition-structure correlation in a phenylalanine-based polymer-silica composite by surface-initiated atom transfer radical polymerization

A polymerizable l-phenylalanine-derived monomer (N′-octadecyl-N^α[4-(acryloyloxy)-butanoyl]-l-phenylalanineamide (3)) has been newly synthesized and characterized. We reported an advanced approach to molecular shape recognitive hybrid materials that involves immobilization of radical initiator on mesoporous silica particles (average diameter, pore size and surface area are 4 μm, 12 nm, and 300 m² g⁻¹, respectively) and surface-initiated atom transfer radical polymerization of monomer 3 from initiator-grafted particles. All samples were characterized by elemental analysis, thermogravimetric analysis, diffuse reflectance infrared Fourier transform spectroscopy, solid state NMR measurements (¹³C CP/MAS NMR and ²⁹Si CP/MAS NMR), differential scanning calorimetry and scanning electron microscopy. The obtained polymer-silica hybrid material was used as a stationary phase for reversed-phase high performance liquid chromatography (RP-HPLC) to investigate its molecular shape recognition ability towards polycyclic aromatic hydrocarbons (PAHs). The new composite material showed better planarity selectivity than octadecylsilane stationary phase as a conventional RP-HPLC packing material and also enhanced linearity selectivity compared with the recently reported poly(N′-octadecyl-N^α-(4-vinyl)-benzoyl-l-phenylalanineamide)-grafted silica. Such selectivity enhancement can be attributed to the combination of hydrophobic effect due to octadecyl chains and multiply carbonyl π-benzene π interaction between the amide groups of the stationary phase and delocalized electrons of PAHs.